Sucrose is a disaccharide whose molecular structure is shown as FIG. 1. (In the FIGURES showing the molecular structure of sucrose and derivatives thereof, the conformational formula is used. For convenience, the hydrogen atoms bonded to the carbon atoms in the two rings and the position numbers of the carbon atoms are shown only in FIG. 1.) The sucrose molecule contains three primary hydroxyl groups and five secondary hydroxyl groups. Therefore, when it is desired to prepare derivatives of sucrose involving reaction of the hydroxyl groups, it can be a major synthesis problem to direct the reaction only to the desired hydroxyl groups. For instance, the artificial sweetener 4,1', 6'-trichloro4,1', 6'-trideoxyoalactosucrose is derived from sucrose by replacing the hydroxyls in the 4, 1', and 6'positions with chlorine. (In the process of making the sweetener, the stereo configuration at the 4 position is reversed hence the compound is a galactosucrose.) This compound and methods for synthesizing it are disclosed in U.S. Pat. Nos. 4,343,934, 4,362,869, 4,380,476, and 4,435,440. The direction of the chlorine atoms to only the desired positions is a major synthesis problem, especially since the hydroxyls that are replaced are of differing reactivity (two are primary and one is secondary; the synthesis is further complicated by the fact that the primary hydroxyl in the 6 position is unsubstituted in the final product). The preparation of this sweetener is only one illustration of the synthesis of sucrose derivatives wherein it is desired either to derivatize certain specific hydroxyl groups, and only such hydroxyl groups, or to derivatize only a specified number of the hydroxyls, perhaps in this latter case without particular regard to which particular hydroxyl(s) are derivatized. The preparation of sucrose-based mono-ester surfactants is a commercial example of mono substitution on the sucrose molecule.
This invention provides a means for synthesizing sucrose compounds such as 6-substituted sucrose derivatives wherein the process of the invention is highly regioselective both with regard to directing the reaction strictly to the 6 position and to the preparation of mono-substituted derivatives only. The term "regioselective" refers to a reaction that highly favors a single major product. Ref., Hassner, "Regiospecificity. A Useful Terminology in Addition and Elimination Reactions", J. Org. Chem., 33. No. 7, 2684-6, July 1968.)